Hip prosthesis implantation requires a stable pelvic foundation, which may be lacking in patients with complex pelvic abnormalities (e.g., arthrodesis conversion, tumour excision, or revision with large bony defects). Many reconstructive options exist for these situations, but their outcomes vary with the initial amount of bone loss and with the technique used. We describe a two-stage arthroplasty technique (acetabular cup first, then femoral stem) and report its use in a case of arthrodesis conversion with concomitant treatment of pelvic and acetabular non-union. Clinical and radiological outcomes after 5 years are reported. This procedure can be adapted to the most complex cases of pelvic reconstruction.